Pollinators are in trouble and ecologists are scrambling to try to keep populations healthy. Economically this matters since a serious decline in pollinators has the potential to doom much modern agriculture but, just in case the ecologists fail, engineers are getting ready to handle the problem. Interested in creating pollinators from tiny drones, a team of researchers has designed and synthesised ionic liquid gels that will allow pollen to stick and be transported artificially.
Honey bees get covered in pollen when they enter flowers to collect nectar and then drop that pollen off in other flowers as they forage. This pollination allows plants to sexually reproduce and is vital to their survival. To date, nobody has been able to find a substance similar to honey bee fur that could readily capture and release pollen grains but the researchers behind the new work suspected that they could manufacture such a substance with ionic liquid gels.
Ionic liquid gels are composed of electrolyte liquids trapped inside solid polymers. They are often electrically conductive, sturdy and have highly variable adhesive properties. This led the team to wonder whether it might be possible to create an ionic liquid gel that was sticky enough to collect pollen grains upon initial exposure to them but then capable of dropping the grains a minute later just as honey bee fur does as the insects rummage around inside flowers.
To test this idea out, the researchers used an acrylic to polymerise an imidazolium salt, which is well known to function as an effective ionic liquid, by baking a mixture of the materials in an oven at 80˚C. Once the ionic liquid gel formed, they measured its tackiness with a probe by monitoring how much load it took for the gel to adhere and how much load was needed for the gel to release the probe once it was stuck to it. This test revealed that the gel was able to rapidly adhere under a very light load but would then release just as quickly when the same small load was applied in reverse. Crucially, the gel did not lose its adhesive properties after multiple attach and release events.
Encouraged by these findings, the researchers applied the gel to horse hairs collected from paint brushes and then attached these hairs to their drones. They then manually piloted the drones to the flowers of the Japanese privet where they guided them to stick the hairs into the male and female organs of the plants. They studied the gel-coated hairs under the microscope between many of the flower visits and confirmed that they were getting coated in pollen. They then used fluorescent microscopy to confirm that pollination was indeed being initiated in the flowers that their drones visited. An abridged version of the research can be found in The Economist article that I wrote on this here.